Sextant attachment



2 Sheets-Sheet 1 Filed April 5, 1948 W M b\ w m a w 3 M U i o Q nm. \0&\ W I I u N. d? U March 6, 1951 c, w,' BALDQCK 2,544,441

SEXTANT ATTACHMENT Filed April 5, 1948 2 Sheets-Sheet 2 awe/who?fatentedl Viar. 6, 1951 UNIT-ED s'mrss PATENT or ce I ,:[flfe T1. S X ANP A W NI Charles wesleyjlialdock; westtlllaj,"

Anne-mu Ann e, 194, :erial-No. 19,021, g

'This "invention relates to sextants. eare .qe ia e. err appe r in e taltitudes of ce stial bodies'which can be calculated and rob eerrti eieiiel to give We e i esl iie re; i. f.

For Sun or Moon For Star or Planet lndex err or' s Indexerror DIP(height of ey' correction) I DIP (height oi eye correction) Refraction rRefraction Parallax Semi-diameter i; sists of the novel construction,combination and arrangement of parts, as will be more specificallyreferred to and illustrated in the accompanying drawings, but it is tobe understood that changes, variations, and modifications maybe resortedto which, fall within the scope of the invention as The presentinvention relates to corrections for Index-Error, called Index-Correction, orIC of a sextant which is the error of its indication's"'due to the 'fact that when the index and horizon'r'n'irrorsar'eparallel, the zeroof the micrometeradjustment does not coincide with thezero of the altitude scale. IC may be caused by a number of conditions,such as rough 'usage of the sextant by jarring the same when putting itin it's-box,

laying the sextant down too hard on the chart desk; or bumping mirrorsagainst some object. Taking the index error out of a sextant isotdiffi'cult when a persori' knows how to do it,- t is ifiicult and hardto explain and also hard low---instructions, "and in additionconsiderable p'r'a fe is required} Where the index error is let in asextant, extra figuring is required each time a sight is taken, and theehances of error are increased in additionto requiring extra timetoget'thepositioni It is, therefore, an object of this invention toprovide an attachment for a sextant which will eliminatethe Ichancesoferror in calculations, and shorten} the time for'getting theposition; 1 'Another object of this invention is to provide anattachment of this kind which can also be combined with the DIPiheightof eye correction) so thatthe index arm can be adjusted inone movementthereofby means of the micrometer adjustment wheel to provide for both,10 and DIP corrections.

A further object of this invention is to profvido an attachment whichwill permitreading the true altitude directly fromLthe sextant andwill'elirninatethe study of reference books and tables claimed. v v V In thedrawings: v l s Figure 1 is a fragmentary side elevation, partly insection, of a sextant having an attachment constructed according to anembodiment of this invention, mounted thereon.

Figure2 is an enlargedsectional view taken on the line 2- -2,ofFigure 1. v Figure 3 is a detailed side elevation, partly inlongitudinal section, of the attachment in applied os on c Figure ;4 is;a-sectional view taken on the line 4-4 of Figure 3, v v

Figure 5 isa detailed end elevation of the adjustable pointer. -Refeiringto the drawings, the numeral in designates generally a sextantwhich includes an arcuate or segmental index are or bar I I over whichan index arm I2 isadapted to be moved. The index bar H is formed withfragmentary threads l3 extending longitudinally thereof which areengaged by a worm l4 carried by a worm or micrometer-adjustment shaftl5. Thevindex arm 12 adapted to be roughly adjusted by means of aspring-pressed release member it which is carried by thearm ,l2andrengages the micrometer orjfine adjustment structure including theworm and: the shaft I5 for disengaging the worm from the fragmentarythreads l3. The worm shaft I5 has mounted thereon. an index wheel I!carrying graduations l8. The structure hereinbefore described isconventional structure in a sextant. v U

It is well known I that in sextants there is an error commonly known asan index error which may be caused by rough usage of the sextant or byother factors. This error can be readily calculated and while it may bea relatively small error, nevertheless, this error entering into thecalculations associated with the'use of the sextantproduces an error inthe final calculations {as to position. In order to provide a meanswhereby the index error or correction may be in 'corporated in all ofthe calculations associated with the sextant, I haveprovided anattachment which includes a-pointer I!) which is carried bya fasteningmeans 23 to a supporting arm 24. The supporting arm 24 is secured byfastening means 25 to the bearing 111g 26 for the micrometer adjustmentshaft I5. The split ring 20 i formed with a peripheral groove 21 withinwhich an adjustable segment 28 having a groove 29 loosely engages. Theadjustable segment 29 has secured thereto a pointer 30 which isconnected with the segment 28 by means of a connecting arm or bar 3|.The pointer I9 is secured to a lug 32 which is carried by asector-shaped plate 33 fixed relative to or formed integral with thesplit ring 20. The adjustable pointer 30 is secured in ad: justedposition relative to the pointer I9 by means of a set screw 34 which isthreaded through the lug 32 and is adapted to engage inthe groove 29;.An enlarged knob 35 is carried by the outer end of the set screw 34 andprovides a means whereby the set screw 34 may be tightened or loosenedand also provides a means whereby the two pointers I9 and 30 may becircumferentiallyadjusted as a unit relative to the micrometer ad.-justment index wheel I! and the graduations I8 on the wheel I'I.

The arcuate index bar II on the side of this bar opposite from normalgraduations carried by this bar over which the index arm- I2 engages isprovided with graduations which include an arcuate series ofcalculations 36 indicating thecorrections necessary in the calculationswhen a star or planet is sighted by the instrument, the calculations 36being minus calculations. A second series of calculations 31' are alsoprovided on the bar I I which are plu calculations and are to be usedwhen sighting the sun. A third series of calculations 38 is provided onthe bar- H in-. dicating the minus corrections necessary.- for height ofthe eye and a fourth series of calculations 39 is provided on the bar IIindicating the height in feet of the eye. The calculations 39 arecorrelated with the" calculations 38 so that when the height ofthe eyeisdetermined the-necessary minus calculation may be made toprovide forcorrection in the calculations for height of the eye.

A pointer 40 is fixed to the index arm I2 being carried by a base 4Ihaving; a, right angular arm 42. The pointer 4|] is adapted to move overthe graduations 36 which include lead lines 43 and outer graduations 44xIn the use and operation of this device the pointer 30 is initiallyadjusted relative to. the pointer I9 to show the corrections normallyappearing in the calculationsfor height of eye. and also for index errorwhich appears. in the instrument. In the present instanceit. isassumed.that the error in the: instrument is. 1.5 and assuming that the heightof the eye is 4.9, pointer 30; isadjusted from pointer I9. a. distanceof 6.4. Where a. planet or star is being sighted. this factonwill be aminus factor. The instrument. is sighted and initially adjusted in thenormal manner, the micrometer wheel being adjusted to provide forregistering or matching of the. two images which are viewed through thesight. After the. index arm I2 has been properly adjusted in. the normaland conventional manner, adjusting. knob 35 is moved so as to positionpointer 30 at the. nearest indication I8 on wheel I'I. Inasmuch as thenumeral 6.4 is a minus. numeral or correction, micrometer wheel I1 isreversed soas to reduce the calculation appearing on the opposite side;of

index bar II which is indicated by index arm I2.

The. wheel I! is reversed in its rotation from the point where pointer30 was set with respect to the graduations I8 so that the 5 graduationwill ment is then viewed on the opposite side of bar I I and thegraduation indicated by index arm I2 and micrometer wheel I! will givethe correct position without the necessity of setting down the initialcalculation indicated by the index arm I2 and then subtracting the indexcorrection factor and the height, of eye;- factor from the sightedindication.

.As an example of the use of this device, where the sun is sightedthe'following calculations were determined from a vessel which was indead reckoning position at latitude 24-10.2N, 8l-30.6W. The line ofposition with a conventional sextant indicated, the; followingcalculations on the sextant:

Hs 66-33.4 The following calculations were also: determined:

1'""f----:?1-:--1-1-e-r-: C T.. \T T5" Monthly sun corr Ht. eye or DIP4.9,

Inasmuch as "the sighting of the sun gives, a plus. factor to theinstrument 12.5 is added. to the initial calculation'of 66-334 giving aHO 6645.9. The above calculations are made on paper and from graduationtables convention in Air and Nautical- A manacs: and a l line of psition b ic W th the u e o the: t achment her nbei re described, theplus factor 12.5 is initially deterined and. s up with. respect t0.- heant n .0- h instrum nt is. th n iewed: n. the no mal manne and hen h obic ive as b en s hted. po nter 30. is ad sted o. the osest 5 ra ua i nI8. he eu n. whe l. I1 s. r at d a r ion; to i crea e. the ca cul ind atby index r nt e. ppo i ide o ba II h h i shown in F re -I Th inst um ntwi h t e. a t hmen will uit sl and accu te y w h: out t e us o pape wkat t e me us n the nstru en ive the orrect s h-tins p i on; in ersubstantiall ss: ime han he; alculat ons-w ic a e. bta ed. b a r mentwhich d es ot ha this atta hmen ther on:- Th s .attachme tmav bem un edon ny convent na s xtan without. i t r with; he n nnal n tic 'ng. Qtthe. sext nt.

atta hment to e. micr me er adjus men worm shaft and index wheel of a.sextant; having a b aring t h shaft car ie by t e. index ar isin a suport ns' mfixed tosaid bearin a bear n r nsi y said; pp rtin rm lqqselyen a in bQ t s hat adi cent to said w ee spl in ti t o al v en agi a o ti ear n rin a d formed. with a h r pli m gr ve. a rst oin r rrie b saidpl r a. s g t memb r ng g n aid. gro ve and s id bl her na. a s c mli pinter carried b sa d egm nt e er.. and, lac in means carried by saidsplit ring and engageable with said. segmental member for selectively,preve tin m cnof said sp i ing and a gmental member relative. to. each.other whereby e d and second. point r m b ad us ed rela t a h. ot r n ta nit r ative. to said wheel.

E LEY'BAL QCKL lReferences on following page) 6 REFERENCES CITED NumberName Date The following r 'eferences are of record in the 1949'908 F1934 file of this t 2,186,553 Lmde Ctr a1. Jan. 9, 1940 2,231,609Anderson Feb. 11, 1941 UNITED STATES PATENTS 5 2,273,956 Hall Feb. 24,1942 Number Name Date ,413,214 Carlson Dec. 24, 1946 100,821 Tuttle Mar.15, 1870 2,420, 39 Leonard May 13, 1947 765,426 Herfick Sept. 12, 19032,439,102 Rothweller Apr. 6, 1948 772,588 Timfall Oct. 14, 1904 ,44 ,94Edelen July 27, 1948 918,709 Smifih Apr. 20, 1909 10 2,463,649 ShiflieldMar. 9, 1949

